Bosse_B
Posts: 966
Joined: Thu Jan 30, 2014 9:53 am

Do I need to remove fake-hwclock if I use an RTC chip?

Wed Nov 13, 2019 9:13 am

I have read a number of howto's regarding use of an RTC module (using the DS3231M chip).
In some they mention the removal of fake-hwclock and in some this is not mentioned.
THIS is a howto where they mention the removal..

What gives here?
If I do not remove it what are the ramifications?
And if I do remove it and the RTC chip fails, what will happen?

Can the RPi/Raspbian system still use network time if there is an RTC module present?
And can it detect that it is missing and then fall back to network time and fake-hwclock if no network is present?

Concerning installation of the RTC this is the procedure as far as I have understood it from several combined howtos:

Code: Select all

sudo apt update
sudo apt upgrade
sudo apt install i2c-tools
sudo raspi-config
#Here enable I2C using 5(Interfacing options)/P5(I2C)
sudo nano /boot/config.txt
#Add the following line to the position towards the end where other similar lines are present:
dtoverlay=i2c-rtc,ds3231

sudo shutdown
#Now unplug power and install the RTC module on the 40-pin header
#start the RPi again by applying power
sudo i2cdetect -y 1
#There should be an entry in the map at address 68 (either 68 if the RTC kernel module is not running or UU if it is)
#Here is where some HOWTO pages start discussing removal of fake-hwclock....

sudo hwclock -D -r
#This should get the current time from the RTC (in debug mode so more info is shown)
date
#If the date command shows the correct time but the hwclock does not then the RTC clock can be set:
sudo hwclock -w
# Done!
If you see a flaw in the procedure above, then please tell me!
I am putting this in my RPi installation notes for future reference...
Bo Berglund
Sweden

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